The fundamental structural frequencies of a typical automobile body are generally a function of its overall dimension, i.e., length width and height. As car sizes are reduced the structural frequencies correspondingly increase. The typical engine for the "downsized" cars is a four cylinder engine. These engines cause the vehicle body structure to be excited by the engine firing pulses through the engine mounts. When the engine pulses substantially coincide with the fundamental body structural resonance, objectional vibrations or resonant shake of the body may be felt by the operator in the steering wheel, floor pans, seat or other body components over the normal idle speed range of the engine.
The most common solution to such resonant shake problems involve isolating the engine from the body and frame by low rate engine mounts. Such engine mounts, however, at some point become impractical due to excessive engine deflections.